It is generally known by those practicing antenna design that a flat microstrip dipole antenna arranged parallel to and in close spaced relationship with a ground plane conductor will exhibit a broadside antenna pattern, that is, a generally hemispherical antenna pattern on the dipole side of the ground plane forming the flat side of the hemisphere. If, however, two or more such dipoles are arranged parallel to the ground plane in the same close spaced relationship with the ground plane conductor, separated from one another by approximately one half wavelength (center to center) and fed with different phases of the same signal, the array of dipoles will form a narrower beam in a direction determined by the phase. Such an array is commonly referred to as a phased array antenna.
Size, weight, cost and signal loss are primary parameters of interest for designing phased array antennas, particularly with respect to conformal antenna systems. For example, mobile antenna applications need low profile, directional antenna configurations that can conveniently be made to conform to the shape of a mobile unit while providing excellent beam steering and electromagnetic properties. Additionally, safety, fuel economy, and freedom from vibration have become important factors in vehicle mounted antenna design, particularly on vehicles intended for use at higher speeds. Conventional projecting-type antennas mounted commonly cause drag to the vehicle and vibration to the antenna while the vehicle is in motion.
Hardware including relatively bulky and expensive discrete elements is typically required to mechanically or electronically steer the resultant beam, thus causing additional problems with respect to size, weight, cost and loss. Electronic steering is conventionally accomplished by means of individual electronically controlled phase shifters (such as ferrite phase shifters or digital delay lines) associated with each element of a phased array to steer the beam by progressively shifting the phases of the signals radiated by the individual radiators.
What is needed therefore is a conformal phased array antenna system that does not require bulky and expensive phase shifters and that is nevertheless capable of providing controlled phase shifts between elements in the array to electronically steer the beam.